Better cancellation of Zarr uploads

[jwodder]

Closes #1028.

[codecov]

Codecov Report

Attention: Patch coverage is 91.07143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 88.39%. Comparing base (f7bb0a9) to head (0db7ecb).
Report is 1078 commits behind head on master.

Files	Patch %	Lines
dandi/files.py	73.68%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1041      +/-   ##
==========================================
+ Coverage   88.36%   88.39%   +0.02%     
==========================================
  Files          69       71       +2     
  Lines        9066     9141      +75     
==========================================
+ Hits         8011     8080      +69     
- Misses       1055     1061       +6     

Flag	Coverage Δ
unittests	88.39% <91.07%> (+0.02%)	⬆️

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[yarikoptic]

Looks great to me, thank you @jwodder ! To prevent possibly more of "orphaned" uploads, I will also mark this for release.

[github-actions]

🚀 PR was released in 0.43.0 🚀